Non-volatile memory devices, such as universal serial bus (USB) flash memory devices or removable storage cards have allowed for increased portability of data and software applications. Flash memory devices can increase data storage density by storing multiple bits in each flash memory cell. For example, Multi-Level Cell (MLC) flash memory devices provide increased storage density by storing 3 bits per cell, 4 bits per cell, or more.
Storing multiple bits of information in a single flash memory cell typically includes mapping sequences of bits to states of the flash memory cell. For example, a first sequence of bits “110” may correspond to a first state of a flash memory cell and a second sequence of bits “010” may correspond to a second state of the flash memory cell. After determining that a sequence of bits is to be stored into a particular flash memory cell, the flash memory cell may be programmed to a state corresponding to the sequence of bits.
Once memory cells in the memory device have been programmed, data may be read from the memory cells by sensing the programming state of the memory cells by comparing cell threshold voltages to one or more read thresholds. However, sensed programming states can sometimes vary from the written programming states due to one or more factors, such as data retention and program disturb conditions. Read thresholds can be updated to reduce a number of data errors resulting from sensed programming states that do not match written programming states. However, read thresholds that are selected to reduce errors in one portion of a memory may cause an increase in errors when reading data from another portion of the memory